In the conventional Fourdrinier papermaking process, a water slurry, or suspension, of cellulosic fibers (known as the paper “stock”) is fed onto the top of the upper run of an endless belt of woven wire and/or synthetic material that travels between two or more rolls. The belt, often referred to as a “forming fabric,” provides a papermaking surface on the upper surface of its upper run which operates as a filter to separate the cellulosic fibers of the paper stock from the aqueous medium, thereby forming a wet paper web. The aqueous medium drains through mesh openings of the forming fabric, known as drainage holes, by gravity or vacuum located on the lower surface of the upper run (i.e., the “machine side”) of the fabric.
After leaving the forming section, the paper web is transferred to a press section of the paper machine, where it is passed through the nips of one or more pairs of pressure rollers covered with another fabric, typically referred to as a “press felt.” Pressure from the rollers removes additional moisture from the web; the moisture removal is often enhanced by the presence of a “batt” layer of the press felt. The paper is then transferred to a dryer section for further moisture removal. After drying, the paper is ready for secondary processing and packaging.
Typically, papermakers' fabrics are manufactured as endless belts by one of two basic weaving techniques. In the first of these techniques, fabrics are flat woven by a flat weaving process, with their ends being joined to form an endless belt by any one of a number of well-known joining methods, such as dismantling and reweaving the ends together (commonly known as splicing), or sewing on a pin-seamable flap or a special foldback on each end, then reweaving these into pin-seamable loops. A number of auto joining machines are available, which for certain fabrics may be used to automate at least part of the joining process. In a flat woven papermakers' fabric, the warp yarns extend in the machine direction and the filling yarns extend in the cross machine direction.
In the second basic weaving technique, fabrics are woven directly in the form of a continuous belt with an endless weaving process. In the endless weaving process, the warp yarns extend in the cross machine direction and the filling yarns extend in the machine direction. Both weaving methods described hereinabove are well known in the art, and the term “endless belt” as used herein refers to belts made by either method.
Effective sheet and fiber support are important considerations in papermaking, especially for the forming section of the papermaking machine, where the wet web is initially formed. Additionally, the forming fabrics should exhibit good stability when they are run at high speeds on the papermaking machines, and preferably are highly permeable to reduce the amount of water retained in the web when it is transferred to the press section of the paper machine. In both tissue and fine paper applications (i.e., paper for use in quality printing, carbonizing, cigarettes, electrical condensers, and the like) the papermaking surface comprises a very finely woven or fine wire mesh structure.
Specifically regarding forming fabrics, these fabrics typically include two layers. The first layer is a top or paper-side layer that includes top warp yarns and top weft yarns that weave with the top warp yarns. The paper-side layer contacts the paper web as the paper web is formed during the papermaking process. The second layer is a bottom or machine-side layer that includes bottom warp yarns and bottom weft yarns that weave with the bottom warp yarns. The machine-side layer contacts various components of the papermaking machine, such as rolls that support the forming fabric, during the papermaking process. In addition, forming fabrics also include binder wefts that weave with both the top and bottom warp yarns to connect the paper-side and the machine-side layers. The binder weft yarns and the top weft yarns typically include long weft floats over the top warp yarns to provide a generally continuous paper-side surface on which the paper web is formed. However, the long weft floats prevent the binder weft yarns from effectively interweaving with the top and bottom warp yarns, and therefore, the stability of forming fabrics is relatively low.
Considering the limitations of previous designs, it would be desirable to have a forming fabric with increased stability and a generally continuous paper-side surface on which a paper web is formed.